Looking at various coverage sources, Commnet appears to be the only company that provides any native service at that remote location. It seems to be only 3G, at that. You could get a prepaid SIM from their retail brand, Choice WIreless. They start at $20 with about $10 extra for every 3 GB of data. There's a dealer in Winnemucca, NV, and another in Lovelock. AT&T Prepaid's coverage map is blank at this location. So, it looks like AT&T prepaid would have given you no service at all.

The US actually has a number of smaller, independent, carriers that serve remote areas. Having very few customers, they survive on government subsidies and roaming fees. Commnet is one of these. Few of these companies have any international roaming partners.